The present physiological study will examine some fundamental aspects of bubble formation in gas supersaturated in vitro and in vivo systems, and will contribute knowledge to the problem of air embolism during decompression from hyperbaric pressures. The first phase of this study will be concerned primarily with in vitro systems. Laboratory experiments will be conducted to determine the supersaturations required for spontaneous bubble formation for a variety of gases andliquids under various conditions. With the exception of preliminary data described here, little or no such information has been available hitherto. The factors which affect this bubble formation, such as the physical and chemical properties of the liquids and the gases, the temperature, etc., will be examined in detail in order to establish a basis for a theoretical formulation of the cavitation events. With this necessary background information, the second phase of the study will examine various aspects of the bubble formation as it relates specifically to in vivo systems. In vitro experiments will be conducted on components of biological systems, such as blood, plasma, solutions, suspensions, interface systems, etc. The investigations will be extended to include the conditions for intracellular bubble formation in laboratory animals, with the goal of increasing our understanding of the etiology of air embolism and, ultimately, of aiding its prevention and treatment by contributing to the development of better hyperbaric gas mixtures and decompression procedures.